1. Field of the Invention
The present invention is applied to a driver of an image display device and relates to a driver for a bidirectional shift register in which the propagation direction of pulse signals can be switched between the forward direction and the reverse direction.
2. Description of the Related Art
In image display devices typified by liquid crystal displays and organic EL display devices, a shift register has been widely used in a signal line driver which generates timing signals for sequentially driving signal lines or a scan line driver which generates scan signals for sequentially driving scan lines.
In various recent instruments such as mobile phones and electronic viewfinders for video cameras, a liquid crystal display device is often used for displaying an image. Further, many instruments have been developed which include rotation mechanisms for rotating the orientations of liquid crystal display devices in order to improve ease of use. In each of these instruments, it is desired that an image inverted vertically or horizontally be displayed according to the rotation angle of a display screen.
A liquid crystal projector includes a separation optical system which separates light from a light source into three primary colors, three light bulbs which control the separated lights according to an image, a combining optical system which combines the controlled lights, a projection optical system which enlarges and projects the combined light, and the like. These optical systems combine images formed by the light bulbs using a plurality of mirrors. However, since the number of mirrors used in each light bulb is different from each other, it is necessary to invert the image of a specific light bulb.
Moreover, the liquid crystal projector projects the combined image onto a screen. Methods for this projection include front projection in which the image is projected from the front side of the screen and rear projection in which the image is projected from the back side of the screen. In both cases, the image needs to be inverted.
The inversion of the image is realized by using a bidirectional shift register in a signal line driver in the case of horizontal inversion or in a scan line driver in the case of vertical inversion. As a bidirectional shift register, for example, one described in Japanese Unexamined Patent Publication No. Hei 10-74062 has been known.
However, known bidirectional shift registers require complex circuit configurations. This causes an increase in the number of interconnections, an increase in circuit scale, and an increase in power consumption. Further, since a first frame of a moving video picture immediately after the switching of the propagation direction of pulse signals is interrupted, the video cannot be displayed smoothly. Furthermore, since complex timing control is required in the switching of the propagation direction, timing design for the controller is complex.